They are designed for different styles of vaping; I'm a mouth to lung vaper, in other words, I like to vape like I used to smoke. Sub-ohm/high wattage tanks are designed for vapers who lung inhale; they have much more airflow, use thicker-gauge wire for their coils, require more wattage to heat up those massive coils, and use much more ejuice...
I like my Emow Mega a lot--BTW, Kanger just introduced OCC (organic cotton coils) for Aerotanks and Emows (you can find them at Sweet Vapes). I also like Eleaf GS Air tanks--very inexpensive (10 bucks for a glass tank) and even better than Kangers, IMHO. Plenty of vapor, great flavor, easy to use--what's not to like?